For the last four years, cloning technology and the discovery of a series of restriction endonuclease enzymes have had a tremendous impact on molecular biology. The use of recombinant DNA techniques has already been very important in the advancement of fundamental knowledge and understanding of the structure and function of genes. This technology provides a way to isolate large quantities of specific segments of pure DNA. Methods for purification of specific genes rely mainly on the technique of hybridization (to a specific probe). Therefore, progress in this important research depends to a great extent on the availability of nucleic acid probes. The specific research goals covered by this grant are these: 1. Chemical synthesis of a mixture of oligodeoxyribonucleotides of sequences predicted from the primary structure of specific proteins (for example, H-2 and HLA antigens, insulin) to establish a screening technique of cloned DNA fragments. 2. Chemical synthesis of a mixture of polydeoxyribonucleotides with sequences complementary to regions of mRNA and its transcript (cDNA) predicted from the primary structure of specific proteins (H-2 and HLA antigens, insulin) to establish a general method for the purification of mRNA and cDNA. 3. Chemical synthesis of all 64 codons in large quantities to allow rapid and efficient synthesis of the oligonucleotides mentioned above.